There are two specific aims in this proposal. (1) Examine the validity and clinical significance of physiologic concordance as a measure of the patient-therapist relationship during psychotherapy. A sub-analysis of existing audio-video recordings of 17 unique patient-therapist psychodynamic psychotherapy sessions is proposed. Moment-to-moment patient-therapist interaction during 3-minute segments of high versus low physiologic concordance will be analyzed with the Bales Interaction Coding System by blinded observers trained to reliability. It is hypothesized that moments of high physiologic concordance will have increased frequency of positive social-emotional categories and decreased frequency of negative social-emotional categories compared with moments of low physiologic concordance. (2) Compare the candidate developed algorithm for measuring physiologic concordance with other established time-series statistical techniques to determine whether the novel algorithm proposed by the candidate is more strongly correlated with patient ratings of therapist empathy. This research has the potential to improve our empiric understanding the patient-therapist relationship in the common intervention of psychotherapy for mental illness.